Many aircraft include one or more auxiliary power units (APUs) to supplement main propulsion engines in providing electrical and/or pneumatic power. An APU may also be used to start the propulsion engines. An APU is, in most instances, a gas turbine engine that includes a combustion section, a power section, a compressor section, and a shaft. The compressor section typically includes an impeller and a compressor. During operation of the APU, air enters through an inlet and is driven by an impeller into the combustion system. The combustion system receives fuel from a fuel source and ignites the compressed air driven therein to produce combusted air. The combusted air produces a thrust that causes the turbine section and shaft to rotate and power a load compressor and generator. The generator supplies supplemental electrical power to the aircraft and the compressor supplies compressed air to the aircraft pneumatic systems. The power from the pneumatic systems may be used to start the main engine or to power air cycle machines in the aircraft that supply air to the aircraft cabin.
In many APU configurations, the compressor is disposed at least partially within a compressor housing that prevents fluids, such as compressed air or lubricants, from leaking into or out of the compressor. The compressor may also include a shaft bearing housing. A seal is typically mounted on the shaft between the shaft bearing housing and the compressor housing that further isolates the interior of the compressor from other aircraft components. In many instances, the type of seal that is used is a knife seal. A knife seal typically includes teeth that are mounted on the shaft and that contact and abrade a coating on the compressor housing when the shaft rotates to thereby seal the interior of the compressor.
During flight operation, the compressor housing and shaft may be exposed to functional vibration. Consequently, the shaft may rub against the housing, and over time, may cause wear and tear on the housing. In the case in which a knife seal is employed, the teeth may dig through the compressor housing coating and cause damage to the housing. When the housing becomes sufficiently worn, it is typically re-coated with the coating material. However, if the housing has suffered extensive wear, it is typically discarded. Unfortunately, a compressor housing is a relatively expensive component to manufacture, and therefore, to replace.
Thus, there is a need for a low cost method for repairing an aircraft compressor housing. Moreover, there is a need for a method of repair that allows an extensively worn compressor housing to be repaired so that the component is salvaged and not discarded. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.